A variety of different types of sheet feeding mechanisms have been previously proposed for a number of different purposes in the prior art. For example, individual sheet feeders are used with conventional photocopying machines to transmit one sheet of paper at a time to the machine from a stack in a cassette. The purpose of these cassettes is to simplify loading and unloading of the sheets and to improve the speed of operation of the photocopying machine or the like.
The previously proposed sheet feeding device generally include a tray or holder of some type, which includes claws or the like arranged to block movement of sheets from the stack in a forward or sheet feeding direction, except to permit movement of only the top sheet in response to a sheet feeding arrangement. Two such devices are disclosed for example in U.S. Pat. Nos. 4,131,274 and 4,033,577.
While these previously proposed devices have been generally satisfactory for use in connection with the feeding of individual paper sheets from a stack, they have not been found by applicant to be satisfactory for use in dealing with special purpose sheets or materials.
In particular, it has been found that it is very difficult to feed or distribute one sheet at a time of microfiche file folders from a stack, other than by manually separating the file folders. These file folders or envelopes specifically consist of two layers of polyester film, such as for example the film sold under the trademark Mylar by the Dupont Corporation which are joined together to form an individual packet, file or envelope. These films are joined together along grid lines which define channels in which microfiche film can be stored. Due to the nature of the film material, there is a substantial tendency for adjacent files or envelopes to adhere to one another in a stack. It is believed that this natural adherence is a result of humidity and static electricity, which forces create an adherence greater than the natural adherence of paper sheets to one another. In addition, because of the smoothness or slickness of the envelope surface, it is difficult to keep the envelopes aligned during movement. Thus, it has been found that conventionally proposed sheet feeding mechanisms for paper stacks are unsatisfactory in handling stacks of microfiche files, folders or envelopes.